A multi-core microprocessor is a computing component that has two or more generally independent processing units or processor cores that read and execute program instructions. Manufacturers typically integrate the cores onto a single integrated circuit die or, alternatively, into multiple dies in a single integrated circuit package. For example, the Apple A5 system-on-a-chip (SoC) designed by Apple, Inc. of Cupertino, Calif. contains a dual-core central processing unit and a dual-core graphics processing unit.
To reduce leakage power on inactive cores, multi-core systems use the concept of power gating where the supply of power to a particular core is cut off by a power gate, such that the core power supply voltage will decay to essentially zero volts. A remaining active core may continue to be supplied with an appropriate voltage level at its power supply input. The power gate is coupled in series with and between the power supply and either a power supply pin or a ground pin of a core, in order to provide power to the processing core. The power gate of each core is typically made of a large number of solid state transistor switches that are connected in parallel and that are controlled together, by some sort of a power manager block or program routine.
The power supply circuit typically used to power a multi-core microprocessor is a regulated, switch mode DC power supply that is designed to deliver the needed current to power a particular core that is active, while maintaining the core supply voltage at a regulated DC level. The regulator in the power supply circuit performs a control algorithm that maintains the correct regulation voltage despite varying load current, based on obtaining voltage feedback from the load that it is driving. A voltage sense line from the processing core's supply pin can be routed to the feedback input of the regulator in order to monitor the load voltage and use it to maintain the regulation. This so-called remote or downstream sensing of the load voltage is desirable, because otherwise the power gate and any other parasitic impedance that lies in the path between a regulator pin and a power supply or ground pin of the core will cause an appreciable voltage drop, particularly at high current, thereby reducing the power supply voltage provided to the processing core (if a local sense point were used for the feedback input).